Various types of apparatus have been proposed to catch, or seize torn portions of a paper web passing through a web handling machine, typically a printing machine. The referenced German Patent DE PS No. 21 56 505 (to which British No. 1,408,176 corresponds) describes an arrangement in which a pair of clamping rollers are provided which are driven continuously in synchronism with rotation of rotary elements of the printing machine. In normal operation, the rollers are spaced from each other, and the web, usually freshly printed and still having wet ink thereon, is passed between the rollers without contact therewith. If the web should tear--signal led, for example, by any well-known and customary tension sensing apparatus--the rollers are moved towards each other to clamp the web therebetween and prevent wrap-around of paper on the printing cylinders of the printing machine, for example around a rubber blanket cylinder thereof. For accurate seizing, the rollers are driven, usually at a circumferential speed which corresponds to about the linear speed of the web passing through the printing machine. When the paper web is to be seized, both rollers continue to be driven. The referenced patent describes a gear train to drive the seizing rollers.
The apparatus permits seizing of webs, however, requires some time to respond. This time may be increasingly long, particularly with high-speed printing machines. It is determined, to some extent, by the inertia of the moving rollers--typically one of the rollers which is pressed against another one which is axially fixed, and, in addition, movement of the drive gearing, or at least part thereof, consequent upon moving of the rollers. To maintain engagement of the respective drive gears for the movable rollers, the drive gears, likewise must be moved.